The invention relates to a fiber-reinforced metal matrix composite material with directionally optimized heat distribution and heat conduction and also to a base plate which includes such a composite material for mounting electrical components and for removing the dissipated power produced by these components to a cooling device.
Electrical components of power electronics and microelectronics include diodes, IGBTs (Insulated Gate Bipolar Transistors) or integrated components which include a multiplicity of electrically interconnected individual components or integrated circuits. These are built up on base plates, which serve both for mechanical attachment and stabilization and for the removal of dissipated heat. With increasing integration and functionality and rising operating voltage, there is an increase in the dissipated power density, that is to say the heat output per unit area, that is produced by the components and has to be removed. Particularly the formation of “hot spots”, that is to say small areas with a high dissipated power density, leads to great thermomechanical loading of the connection setup between the electrical components and the base plate, and consequently to a reduction in reliability. Consequently, the heat removal and heat distribution restrict the maximum attainable dissipated power density, and consequently the possible integration density of components.
Therefore, both the setting-up and connecting technique and the cooling technology are playing an ever more important role in the further development of power electronics and microelectronics. High dissipated power densities can only be cooled with great effort, by active cooling methods such as two-phase cooling or forced liquid cooling. It is therefore necessary to distribute the heat over a larger area and subsequently remove it to appropriate cooling media such as air, oil or water.
In the past, base plates made of ceramic, metals or composite materials, such as for example Cu, Al, Al2O3, AlN, Al—SiC, BeO, Cu—W or Cu—Mo, have been used for removing and distributing the dissipated heat. These materials have an isotropic thermal conductivity in the range from 27 W/m·K (Al203) to 400 W/m·K (Cu). For better removal of the dissipated power, a thermal conductivity of at least 600 W/m·K is desired for a composite material.
The high coefficients of thermal expansion of the previously used base plate materials in comparison with the material of the electrical component lead to stresses in the connection setup between components and the base plate, and consequently to a reduction in reliability.
To solve these problems, highly graphitized carbon fibers have been incorporated in various materials, such as for example C, Cu or Al, on a trial basis, for example by the company Applied Sciences Incorporation. In this case, the fibers had a diameter of several pm and a length of several mm and were isotropically distributed in the matrix material. Thermal conductivities of up to 910 W/m·K were achieved. Similarly, longer fibers and their integration in various materials are known. Methods of incorporating fibers in matrix materials are, for example, liquid phase infiltration, hot isostatic pressing (HIP) or the squeeze casting method.
However, composite materials with an anisotropic distribution, optimized with respect to the heat distribution, of fibers with a high thermal conductivity are still not commercially available or used.
A disadvantage of the isotropic distribution of the fibers in the material, of base plate materials for example, is the insufficient distribution over a large area of the peaks of dissipated heat occurring at “hot spots”, which leads to stresses in the material itself and at the interfaces with other materials and to reduced reliability of the overall setup.
For these and other reasons, there is a need for the present invention.